Heat capacity and thermodynamic functions of zirconia and yttria-stabilized zirconia

Heat capacities of pure zirconia ZrO2 and 7.76.10(-2) mole fraction yttria-stabilized zirconia (ZrO2)(0.9224)(Y2O3)(7.76.10-2) were measured by adiabatic calorimetry at temperatures between 13 K and 300 K. The results were compared and analysed from the standpoint of the effects of yttria doping. The yttria-stabilized zirconia showed excess heat capacity at low temperatures which should be attributed to so-called low-energy modes caused by the defects in the crystal. The smoothed values of molar heat capacities at rounded temperatures were calculated from the experimental data. The thermodynamic functions enthalpy, entropy, and Gibbs free energy were also calculated and tabulated. The standard enthalpy and entropy of pure zirconia and 7.76.10(-2) mole fraction yttria-stabilized zirconia at T = 298.15 K are 8.711 kJ.mol(-1) and 49.79 J.K-1.mol(-1), and 9.595 kJ.mol(-1) and 56.47 J.K-1.mol(-1), respectively. (C) 1999 Academic Press.